Method of monitoring measurements

ABSTRACT

A method of monitoring a system requiring periodic measurements of a plurality of points of the system, includes the steps of identifying deterministic points in the system as those points which are determinative of one or more determined points in the system, collecting measurements from the deterministic points of the system, storing the measurements, calculating a rate of change for each of the deterministic point value using previously stored measurements, calculating a rate of change of determined points from the rate of change of the deterministic points and using the rate of change values for deterministic points and determined points to estimate when an event will occur in relation to each point.

FIELD OF THE INVENTION

The present invention relates to a method of monitoring a systemrequiring periodic measurements of a plurality of points. The presentapplication has many fields of use including systems such as a piece ofequipment, an area of ground, or a manufacturing or processing plant.The areas of applicability of the present invention are not intended tobe limiting.

BACKGROUND OF THE INVENTION

Systems that require multiple periodic measurements generally result ina great deal of effort being required to log, collect and interpret themeasurements. Often it is desired to predict when the measured pointswill reach a predetermined value. Currently the known method of doingthis is to collect all of the data and compare each data value to thepredetermined value.

The present invention provides a more convenient method of monitoringpoints of a system.

SUMMARY OF THE PRESENT INVENTION

According to the present invention there is provided a method ofmonitoring a system requiring periodic measurements of a plurality ofpoints of the system, including the steps of:

identifying deterministic points in the system as those points which aredeterminative of one or more determined points in the system;

collecting measurements from the deterministic points of the system;

storing the measurements;

calculating a rate of change for each of the deterministic point valueusing previously stored measurements;

calculating a rate of change of determined points from the rate ofchange of the deterministic points;

using the rate of change values for deterministic points and determinedpoints to estimate when an event will occur in relation to each point

According to another aspect of the present invention there is provided amethod of monitoring a system requiring periodic measurements of aplurality of points of the system, including the steps of.

identifying deterministic points in the system as those points which aredeterministic of one or more determined points in the system;

collecting measurements from the deterministic points of the system;

storing the measurements;

calculating a rate of change for each of the deterministic point valueusing previously stored measurements;

calculating a rate of change of determined points from the rate ofchange of the deterministic points;

using the respective deterministic point or determined point rate ofchange value to estimate when an event will occur in relation to one ormore of the points.

Preferably the methods include the step of calculating one or moreratios between the rate of change of one or more of the determinedpoints and one or more of the deterministic points, the ratios beingused in the step of calculating the rate of change of determined points.

Preferably the methods include the step of collecting measurements fromone or more of the determined points, less often that the measurementsare collected from the deterministic points.

Preferably the measurements from the determined points are used tocalculate each ratio between the rate of change of each determined pointand one or more of the deterministic points.

Preferably the measurements from the determined points are used tocalculate each ratio between the rate of change of each determined pointand two or more of the deterministic points.

Preferably the rate of change of a plurality of deterministic points areused to determine the rate of change of one or more determined points.

Preferably if the rate of change of one of the deterministic points isnot available the remaining rates of change of the other deterministicpoints are used to determine the rate of change of the relevantdetermined points.

Preferably the rates of change are used to estimate dates when themeasured values reach certain values.

According to another aspect of the present invention there is providedan apparatus for monitoring a system requiring periodic measurements ofa plurality of points, said apparatus including:

means for collecting measurements from a plurality of points identifiedas deterministic points of the system;

means for storing the measurements;

means for calculating a rate of change of each deterministic point valueusing previously stored measurements;

means for calculating a rate of change of one or more determined pointsfrom the rate of change of deterministic points;

means for estimating when an event will occur in relation to one or moreof the points from the respective deterministic point or determinedpoint rate of change value.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to provide a better understanding, preferred embodiments of thepresent invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of a system requiring periodicmeasurements of a plurality of points; and

FIG. 2 is a flow chart showing the steps in the method of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1 there is shown a system 10 requiring the measurementof a plurality of points. The system 10 includes a pump 12, a pipe 14and a tank 16. The pump 12 pumps fluid 18 through the pipe 14 and intothe tank 16. The pipe 14 includes a series of pipe sections 20, 22, 24,26, 28, 30, 32, 34, 36, 28 and 40. Each of the pipe sections is measuredat positions A, B and C along the length of each pipe section. At eachposition A, B and C, four measurement points may be taken at 0°, 90°,180° and 270° around the circumference of the pipe. The characteristicmeasured at each of the measuring points may be, for example, thethickness of the pipe at the measuring point This measurement may betaken, for example, to determine wall thickness if the pipe is subjectto wear or corrosion or the build up of internal scale. It is clear fromthe simple system shown in this example that 12 measurement points aretaken for each pipe section and in this example there are 11 pipesections with the result being 132 measured points if every point ismeasured. By identifying points deterministic of the characteristicbeing measured at other points less points can be measured. In thisexample, measurement position B in pipe section 26, is likely to bedeterministic of other points in the system. As a result, the fourmeasurements at 26B can be measured at the usual frequency ofmeasurement with all of the other points of pipe section 26 beingmeasured less frequently.

Referring to FIG. 2 the method 30 of the present invention is shown. Thefirst step is a collection of data 32. Data is collected by, for examplea data logger, process control equipment or another form of measuringdevice. Generally a large number of points will have data measured,rather than the 132 in the simple example of FIG. 1. Due to the largenumber of data points it is important that data be structured in a waythat simplifies location of a sub-set for analysis. To achieve this,points are located on plant records. Plant records are arranged in arecursive hierarchy so that as many parent/child levels can beconstructed as desired. Plant records are contained within departmentsso that selecting a department reduces the plant records data set tothose that are relevant. Departments are located within sites. Sites arelocated within companies.

Once the data is collected it is uploaded at 34 to a database. Data isoften extracted from collection devices in a variety of formats. Datamust therefore be formatted so that it can be interpreted. Parsing ofthe data preferably extracts the following information:

plant or system code;

point label;

value;

unit of measure;

date of measurements;

flags and miscellaneous attributes.

The extracted data is uploaded to a staging table which is thenprocessed by a plant ID number and point ID number for each measurement.

Data from the staging table is then validated at 36. The data in thestaging table is reviewed to detect unacceptable anomalies. Validationincludes the following checks:

imported data are matched with a plant code and point label in thedatabase of plant names and points;

non-matched data may be stored in a temporary area for later manualprocessing or allocated a dummy plant code and point label for laterinsertion in the plant hierarchy,

certain points are expected to trend upwards over time, taking intoaccount a specified tolerance;

certain points are expected to trend downwards over time, taking intoaccount a specified tolerance;

the department in which the point resides has not been marked to warnwhen important values are zero or to a user defined reject value (eg. insome loggers nonsense data is given the value 99999);

records must have a value that is numeric;

records must have a unit of measure.

Records that fail to meet the first five requirements are returned tothe user for action. Records that fail to meet the last two requirementsare excluded from processing. The user can fix the data value, mark itfor fixing later, indicate that the plant has been altered or omit thatrecord from import into the database, or cease the import, repair thedataset and then import it again.

Data that is imported for fixing later or where the plant has beenaltered will use an historical rate of change and not the one based onthe new measured value.

Pre-processing of the validated data occurs at 38. The data from thestaging table are stored in a readings table with calculations beingperformed on the data in the readings table.

The change in the measured variable between the actual measurementintervals is determined. This is termed Dv. That is, the current datavalue has the previous data value subtracted to determine the change. Dvvalues that trend in the wrong way within a tolerance will be treated asequal to zero. If the point is supposed to trend down and the new Dvvalue is greater than a specified tolerance then Dv for the reading isset to null. Similarly, readings that are expected to trend upwards butreduce in magnitude within the tolerance are set to 0, outside thetolerance are set to null. If a system item is marked as altered duringthe period since the last data input, the Dv calculation is omitted asthe value may not be valid due to the change to the system 10. Analteration may be due to the replacement of a worn part or a change inthe structure of the system.

The change in time between the previous actual readings, termed Dt, iscalculated. This is simply the difference in date/time values betweenthe most recent and the previous readings. Time is typically measured indays although other time units maybe used depending on the application.

The weighted rate of change of the point (Dt/DvWtd) is calculated. Themost recent rate of change (Dv/Dt) is determined by dividing the changein the Dv by Dt. The latest Dv/Dt value along with previous Dv/Dt valuesare used in a weighting profile to smooth out variations in the measuredvariable. The result is stored on the point record. The weightingprofile uses an array of, for example, up to the ten most recent Dv/Dtvalues. The profile to be used for each point is stored in a pointrecord. Each profile in the library of profiles must have a series of upto ten percentages that must add to unity. The simplest of these wouldbe 100% for the latest Dv/Dt value, other examples include 60/40 being60% of the latest 40% of the second most recent values; 70/20/10 or alinear model. A table of example weighting profiles follows: Most recent10 Measurements ago Dv/Dt 0.0112 0.012 1E−04 0.014 0.012 0.043 0.0120.017 0.0.163 0.017 Dv/DtWtd Latest 100 0 0 0 0 0 0 0 0 0 0.0112 60/4060 40 0 0 0 0 0 0 0 0 0.0159 70, 20, 10 70 20 10 0 0 0 0 0 0 0 0.0125Linear 10 10 10 10 10 10 10 10 10 10 0.0167

Any set of historical readings having null Dv values within the (rangeof) profile values (about zero) does not have a new Dv/DtWtd valuecalculated. In this case, the previously calculated value is kept forcalculations. Points in the plant that have been altered during theperiod spanning the weighting profile do not have the Dv/DtWtdcalculated due to the change of system 10.

Each reading is provided with an instance counter for storing respectiveinstances of the data value. Readings on or prior to a plant recordbeing (date) altered have the respective instance counter set to null.Each point has a reference to a weighting profile. Each profile has arecord for the instance and the weighting percentage to be applied. Theresulting value of the weighted rate of change (Dv/DtWtd) for the pointis stored on the point record. Alternatively, the weighted values arecalculated on the fly from stored measurement records.

The weighted rate of change of this pre-processed data is then processedat 40. Points in the same group of a plant are identified as eitherdeterministic (also referred to as signature points) or determinedpoints (also referred to as derived points). All of the signature pointsin groups of data to be analysed should be included in the measuredpoints. In the example shown in FIG. 1, one of the measured points atlocation B of pipe section 26 may be a signature point. In a morepreferred form of the invention any or all of the points at location Bof pipe section 26 may be signature points.

Each signature point is used to derive the other points in the groupthat are not included in the imported data. Again in the more preferredform of the invention, a plurality of signature points are aggregated(such as by taking the average, the minimum or the maximum) to deriveother points in the group. As a result it is not necessary to measureeach of the derived points in the group although some of the derivedpoints may be measured in addition to the signature points in the group.A signature ratio is calculated for each derived point in the group. Thesignature ratio is historically derived from previous group point's rateof change divided by the signature point rate of change. Thus, fornon-measured, derived points in the group the weighted rate of change iscalculated from the signature points weighted rate of change multipliedby the points signature ratio. Points that are calculate are marked ascalculated, whereas points that are measured are marked as actual sothat it is possible to distinguish between the derivation of the rate ofweight of change of each point. Values are stored in a historicalreading table.

In the more preferred version calculated rates of change and determinedpoints are always calculated on the fly.

The processed data is then used to calculate and/or update prognosis ofthe likely time that measurement will reach an alarm value or a criticalvalue. A warning value may also be used. Particular points or everypoint affected by the uptake of readings can be calculated as follows:Warning Date=[Date of Latest Reading]+(([Warning Value]−[LatestValue])/[Dv/DtWtd])Alarm Date=[Date of Latest Reading]+(([Alarm Value]−[LatestValue])/[Dv/DtWtd])Critical Date=[Date of Latest Reading]+(([Critical Value]−[LatestValue])/[Dv/DtWtd])

To ensure that the signature point ratios are accurate an adjustment ofthe ratios occurs at 44. This occurs where points that are actuallymeasured are given the opportunity to adjust the ratio between the rateof change of the measured point and that of the signature point. In themore preferred system the rations are always calculated in real time asneeded. The signature ratio is calculated by dividing the latest rate ofchange for the point by the rate of change of the signature point overthe same period. Since signature points should be measured more oftenthan group points the calculation therefore involves averaging the Dv/Dtvalues for the signature point over the period spanning the two mostrecent group point readings. Since the group points have their own grouppoint readings it is necessary to calculate the signature rate of changeseparately for each group point. The signature ratio for signaturepoints is always unity so that they can be excluded from signature ratiocalculations.

Since the frequency of measuring derived points should be less than thefrequency of measuring signature point and the calculation of alarm andcritical dates can be estimated, scheduling for measurement of pointscan be achieved to provide optimum route selection and/or cost savings,as indicated in 46.

In the more preferred form where multiple signature points are used todetermine the derived points, where one of the signature points isaltered, the remainder of the signature points can be used to derive theratio for the derived point. This overcomes the problem of where asingle signature point is used and is modified (such as when a componentis replaced), a delay occurs until enough data is provided to determinethe weighted ratio for that signature point.

Points are typically measured in predefined sequences that facilitateaccess in the field. Sequences are called routes and are often in anorder that is not simply determined by plant coding. The reason is thatthe routes are often defined by physical access restraints in the field.Any point can reside in the many routes and can be in a differentsequence in each route. Routes are used to export the data to dataloggers in the order that they will most easily be encountered in thefield. This allows the user taking readings to simply enter themeasurement with one press of a button on the device and the next pointis displayed ready for measurement. This greatly speeds up themeasurement process.

Plant items can be selected for export to a data logger by use of adrilldown hierarchy display. Highlighting a record within a hierarchyand selecting the plant item will include all children ancestors of thatitem. Many sections of the plant can be selected one after another.Selected routes and points on the selected plant can be passed onto aselect point for export grid.

A matrix with calculated points, signature points and/or points acrossthe top and points due in alarm and points in critical alarm allow awide selection of points from the plants and routes selected fordownloading. The user can select respective points to download todetermine a route. The export process can filter out desired points andsend them to an export program for downloading to the data logger.

The points for the next reading can then be exported by various meansdepending on the data logger type. After the points are reviewed, theuser can select the type of data logger format for export and then thedata can be downloaded to the data logger.

This process can therefore eliminate points that either do not need tobe measured or can be measured less frequently thus saving time. Inaddition, a plant containing many measurement points, only those pointsthat require measurement such as signature points or derived points thathave not been measured in some time need be included in the route. Thiswill also allow a staggered measuring of derived points, which can bedesigned to suit for example down time in a plant where it is otherwisenot possible, or at least difficult, to gain access to take ameasurement.

The skilled addressee will realise that modifications and variations maybe made to the present invention without departing from the basicinventive concept. Such modifications include the number and nature ofmeasurements taken, the weighting of the rate of change, the data value,the period or frequency of measurement and the application of thepresent invention beyond manufacturing and processing plants.

Such modifications and variations are intended to be within the scope ofthe present invention, the nature of which is to be determined from theforegoing description.

1. A method of monitoring a system requiring periodic measurements of aplurality of points of the system, including the steps of: identifyingdeterministic points in the system as those points which aredeterminative of one or more determined points in the system; collectingmeasurements from the deterministic points of the system; storing themeasurements; calculating a rate of change for each of the deterministicpoint value using previously stored measurements; calculating a rate ofchange of determined points from the rate of change of the deterministicpoints; using the rate of change values for deterministic points anddetermined points to estimate when an event will occur in relation toeach point.
 2. A method of monitoring a system requiring periodicmeasurements of a plurality of points of the system, including the stepsof: identifying deterministic points in the system as those points whichare deterministic of one or more determined points in the system;collecting measurements from the deterministic points of the system;storing the measurements; calculating a rate of change for each of thedeterministic point value using previously stored measurements;calculating a rate of change of determined points from the rate ofchange of the deterministic points; using the respective deterministicpoint or determined point rate of change value to estimate when an eventwill occur in relation to one or more of the points.
 3. A methodaccording to either claim 1 or 2, wherein the method further includesthe step of calculating one or more ratios between the rate of change ofone or more of the determined points and one or more of thedeterministic points, the ratios being used in the step of calculatingthe rate of change of determined points.
 4. A method according to eitherclaim 1 or 2, wherein the method includes the step of collectingmeasurements from one or more of the determined points, less often thatthe measurements are collected from the deterministic points.
 5. Amethod according to either claim 1 or 2, wherein the measurements fromthe determined points are used to calculate each ratio between the rateof change of each determined point and one or more of the deterministicpoints.
 6. A method according to either claim 1 or 2, wherein themeasurements from the determined points are used to calculate each ratiobetween the rate of change of each determined point and two or more ofthe deterministic points.
 7. A method according to either claim 1 or 2,wherein the rate of change of a plurality of deterministic points areused to determine the rate of change of one or more determined points.8. A method according to either claim 1 or 2, wherein if the rate ofchange of one of the deterministic points is not available the remainingrates of change of the other deterministic points are used to determinethe rate of change of the relevant determined points.
 9. A methodaccording to either claim 1 or 2, wherein the rates of change are usedto estimate dates when the measured values reach certain values.
 10. Anapparatus for monitoring a system requiring periodic measurements of aplurality of points, said apparatus including: means for collectingmeasurements from a plurality of points identified as deterministicpoints of the system; means for storing the measurements; means forcalculating a rate of change of each deterministic point value usingpreviously stored measurements; means for calculating a rate of changeof one or more determined points from the rate of change ofdeterministic points; means for estimating when an event will occur inrelation to one or more of the points from the respective deterministicpoint or determined point rate of change value.